Electric bushing and glass therefor



Aug. 9, 1949. w. w. GRIGORIEFF 2,473,626

ELECTRIC BUSHING AND GLASS THEREFOR Filed Sept. 9, 1947 :00 zoo zoo 40c 500 m TEMPERATURE 'c Inventor: Wlactirnir- W. Gr'igor'ieff.

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is Attorney.

Patented Aug. 9-, 949

ELECTRIC BUSHING AND GLASS THEREFOR Wladimir W. Grigoriefl, Fayetteviile, Ark, alsignor to General Electric Company, a corporation of New York Application September 9, 1947, Serial No. 172,983

8 Claims. (01. 174-152) This application is a continuation-in-part of my prior application, Serial No. 710,031, filed November 15, 1946, now abandoned.

The present invention relates to cast glass electric devices, such as insulating bushings, and includes lead-free borosilicate glasses of novel characteristics which are particularly well adapted for sealing into unitary relation with parts consisting oi nickel-iron alloy.

Glasses embodying my invention are characterized by a high degree of fluidity when molten and hence are suited for casting into molds in the fabrication of articles of complex configuration.

Heretofore cast-glass electric bushings have been fabricated by casting lead-containing glass into contact with metal parts. Such bushings are described, for example, in prior Patent 2,299,750 of Hull and Moore patented October 27, 1942. It has been found that metal parts consisting of ferrous alloy when in contact with the molten lead glass enter into a chemical reaction with the glass composition. This causes the deposition of metallic lead on the surface of the ferrous metal, and resulting in inadequate adhesion and faulty sealing between the metal and the glass. It precoat the metal parts to prevent lead deposition, but such operations are complicated, costly and time-consuming. Glasses embodying my invention' can be cast and sealed into direct contact with uncoated ferrous metals without such difllculty.

The lead glass described above has also poor weather-resisting properties. The surface of the glass becomes roughened when exposed to the atmosphere under varying conditions of humidity thereby promoting the collection thereon of dirt and carbon particles. Such deposits reduce the effective creepage resistance of a bushing resulting eventually in electric discharges over the surface of the bushing, with attendant shortcircults and damage to the bushing and other equipment. Glasses embodying my present invention are highly resistant to weathering. Their surfaces remain substantially unaltered even when subjected to prolonged contact with at-- mospheric or other chemically active agents.

Glasses embodying my invention may be considered as soft borosilicate glasses containing chemically combined a total amount of alkali oxide in the range of about 8 to 13 per cent. Although some small changes of composition occur due to. volatilization and other natural causes, the composition of the glass batch (starthas been proposed to protectively ing materials) determines the composition of the resulting glass. The batch ingredients from which the glasses of this invention are prepared combine to form glasses of the following approximate range of proportions indicated:

Ingredients Range Silica-S10 Lithium oxideLi1O a multiconductor type of bushing; and Fig. 3

is a graph showing coeilicients of elongation of glass and metal parts of such bushings.

The bushing shown in Fig. 1 includes a screwthreaded hollow terminal stud l which is brazed to a collar 2, the latter in turn being embedded in a glass insulator 3. This insulator, which embodies the present invention, is cast from fusion to envelop the rim of this upper collar 2 and also the rim of a lower collar 4 which serves as mounting flange whereby the bushing is joined to a container 5 (shown broken away) by soldering, brazing, or welding, thus providing hermeticseals between all metal-to-glass and metal-to-metal joints. A metal tube 6 which is positioned within a metal thimble 1 passes longitudinally through the glass insulators 3. A metal conductor (not shown) leading to the interior terminal of an electric device may be passed through the tube 6. It may be attached to the terminal stud i in any suitable way as by soldering or brazing. The metal thimble I at the upper end of the bushing and the shield 8 within the collar 4 shields portions of the adjoining collars from contact with fused glass during casting thus permitting expansion and contraction of the bushing parts without damage.

In Fig. 2 is shown a modified bushing which comprises three terminal studs 9, i0 and i l which are respectively provided with collars l2, l3 and M. The rims of these collars are similarly embedded in a cast glass insulator it which embodies the present invention. An inwardly projecting flange of the basal collar I6 is embedded in the glass insulator l5 while the latter is cast in the fused state. The flange ll of the collar I6 is joined by welding or otherwise to a container [8 or a capacitor, transformer 01' othe electric device.

The following compositions are illustrative of my invention. The ingredients need not necessarily consist of the indicated oxides in an uncombined state. For example, carbonates of the alkali metals ordinarily are used, the carbonate breaking down thermally to yield the indicated amounts of oxide. The proportions given are for equivalent oxide content. In the third example, color-producting oxides are added:

Proportions in Per Cent by Weight Ingredients Glass No. 2

Glass N o. 3

. pe s s s f zhmtuwoapenhoo Fusion and reaction of the catch ingredients occurs in a suitable glass making furnace, preierably an electric furnace. The resulting fused glass is cast at a temperature of about .1250" into suitable molds provided with desired. metallic inserts. Glass compositions embodying my invention have densities in the range of about 2.36 to 2.38. Metal oodles be caused to be embedded in and to adhere without undesired chemical effects to cast glass so as to an integral part of the finished article. These inserts preferably consist of a metal ha "21g 2. coefiicient of linear expansion of lflifikel ii alloy consisting of 57-59% iron and 43-41% nickel. an alloy oi this composition has a eoeiiicient of linear expan sion of about 5.5x loin the temperature range of 25 to 300 (3.

As the glasses of my invention have closely similar coefiicients of expansion as iron-nickel alloy, a firm. union is maintained between the glass and metal.

The following analyses were made of glasses embodying my invention: fliese analyses are to be considered as illustrative and not as limiting my invention.

Proportions in Per Cent by Weight Ingredients GlassAGlassBGlassO Graph 19, 3 shows the rate of. linear change over an indicated temperature range of an consisting by weight of about 53% iron and 42% nickel. Graph 20 shows similarly the coefllclent of linear change of a glass embodying my invention. These two graphs show that there are some diflerences in the expansion and contraction characteristics of the metal alloy and the glass, the difierences are not great enough to cause cracking or other difliculty in the manufacture of composite metal and glass articles, such for example, as the bushings.

shown in the drawing.

The mixed alkali oxides, and particularly the lithium oxide, impart to the glass a desired low viscosity at a temperature at which the glass may be cast through a. restricted orifice into a mold in contact with metal members for example, when casting glass for insulating bushings such as shown in the accompanying drawing. Such molds may have a maximum pouring opening of to A9," diameter and hence require a highly fluid melt to be east through such restricted ori fices.

The presence of the three alkalies imparts to the glass better weather-resisting qualities than would result if single alkali were present.

Some of the useful properties of borosilicate glass embodying my invention have been de scribed in connection with electric bushings in which such glass constitutes the insulating men.-= ber. glass of invention is not lim ited in its useful applications to electric bushings.

What E claim as new and desire secure by Letters Patent of the United States is:

A glass composition having suficient fluidity when to about i256 to 13% to new when east through. a restricted orifice of about inch diameter and to hermetically seal to metal member consisting oi about ll 43 per cent nickel and 59 to 57 per cent iron, such glass having the following approximate range of com position:

Per cent Silica M 66 to 69 Boric oxide w--- M. 26 to 25 Alumina u a... S to 8 Lithium oxide s... ...-....W---" 5.2 Sodium oxideto d Potassium oxide M l to 5 2. A glass suitable for casting molds com= prisingthe following oxides as essential lngre dients:

Per cent Silica 64.0 Boric oxide- 20.6 Alumina 3.4 Potassium oxide 2.5 Sodium oxi 5.1 Lithium oxide 4.4

3. A glass suitable for casting in molds comprising the following oxides as essential ingredients:

4. A bushing for an electric device comprising insulating member of glass containing the following constituents combined within the indicated range of proportions: silica 60 to 69 per cent, boric oxide 20 to 25 per cent, alumina 3 t 8 per cent, lithium oxide 25 to 5.5 per cent, sodium oxide 3.8 to 6 per cent and potassium oxide 1 to 5 per cent and cooperating electric terminal members consisting of an alloy of 41 to 43 per cent nickel and 59 to 57 per cent iron embedded in part in said glass member.

5. A bushing for an electric device comprising an insulating member of glass containing the following constituents combined with the indicated range of proportions: 1

Per cent Silica 64.0 Boric oxide 20.6 Alumina 3.4 Potassium oxide 2.5 Sodium oxide 5.1 Lithium oxide 4.4

and cooperating electric terminal members consisting of an alloy of 42 per cent nickel and 58 per cent iron embedded in part in said glass member.

63.5 per cent silica, 21.8 per cent boric oxide, 3.5

per cent alumina, 2.4 per cent potassium oxide, 5.4 per cent sodium oxide and 3.4 per cent lithium oxide.

WLADIMIR W. GRIGORIEFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,394,296 Fisher Oct. 18, 1921 2,299,750 Hull Oct. 27, 1942 2,392,314 Dalton Jan. 8, 1946 OTHER REFERENCES Ceramic Industry, January 1944. Pages '14 and 85. 

